Traditional commercial biogas plants are usually fairly big and require huge quantities of energy crops, notably maize. “Maize is very profitable, both in terms of its cultivation, something that farmers have a great deal of experience in, and in terms of the production of methane. In contrast to other plants, maize contains very little lignin. Lignin is a very complex compound and an integral part of the secondary cell walls of plants. Like wood, it can only be degraded under aerobic conditions,” said Michael Schuster, managing director of Konstanz-based n-bio GmbH. As biomass can only be converted into methane in the absence of oxygen, biogas reactors have to be fed raw materials such as maize, which can be degraded in the absence of oxygen. The increasing use of agricultural lands for energy rather than food production is currently a matter of heated debate. “At present, around 10 per cent of agricultural land worldwide is used for the cultivation of energy crops. In future it will be up to politicians to decide whether even more agricultural land will be used for the cultivation of energy crops,” said Schuster. As an alternative, n-bio GmbH is working on ways to generate energy from waste that needs to be disposed of anyway.

The use of waste for energy production is an attractive alternative to the use of energy crops such as maize, not just for the operators of biogas plants but also for waste producers who need to get rid of waste. Waste accumulates whatever happens, it does not need to be grown and it can be used for generating energy. “Biological waste is suitable for use in fermentation plants, but it contains a relatively large amount of woody green waste, which has a negative effect on methane production," said Schuster who studied biology at the University of Konstanz. Attractive sources of green waste are large-scale catering establishments, supermarkets and the food processing industry which discard masses of food every day. Some waste disposal companies therefore construct biogas plants in order to work towards a reliable and economic use of waste. “I believe that biogas plants are the most sensible and the cheapest way of discarding waste. The combustion of waste costs a lot more,” said Schuster. 

However, waste fermentation plants have high technological requirements, as supermarket waste contains energy-rich food as well as plastic packaging, glass, bones and other materials that cannot be digested. “These substances only pose a major problem in the fermentation process when huge quantities are present. But they are more problematic in fermentation residues because they are used by farmers for fertilization,” explains Michael Schuster. n-bio plants are able to separate unwanted material that would otherwise compromise the biogas production process. The n-bio biogas plant operators are able to feed delivered waste into the plants without any extra treatment; sieves and other separators ensure that only the biomass gets through. “We also have plants that are able to process pralines. The devices are relatively efficient in separating the packaging material from the biomass. The only thing that needs to be taken into account is the high costs generated by the large quantity of plastic that needs to be disposed of,” Schuster added.

After fermentation, pathogens need to be removed from the fermentation residues in order to prevent them from being spread on fields when used as fertilizer. And this is exactly what the n-bio biogas plants do. Hygienization is completed as soon as the fermentation residues have been heated to 70 degrees centigrade for one hour. Once this procedure is complemented, the fermentation residues can be further processed in order to remove nitrogen. However, the methods used to do this are rather complex and time-consuming. 

Many biogas plant constructors use standard concepts that involve converting standard liquid manure tanks, to give just one example. However, the disadvantage of this is that the sensitive technology needs to be mounted inside the fermenters, which makes it difficult to access. n-bio GmbH has taken a completely different approach and builds the majority of its plants according to the “Danish” principle, which is less well known. “The agitators and the motor are mounted on top of the fermenter; this provides better protection and also consumes less energy,” Michael Schuster explains. This effective design is more expensive in the short term, and is only profitable for medium-size plants (500 kW or more). But in the end, the extra investment pays off. 

n-bio is working with Konstanz-based bio-ferm Research GmbH and British research institutions in order to further optimize the biogas production process. A number of pilot plants are carrying out pilot experiments on the fermentation of pharmaceutical waste. The first biogas plant of this kind is already being planned and might soon be up and running.

Michael Schuster believes that the biogas market is likely to be confronted with important changes. “There will be a slump in the biogas market in Germany. Everybody agrees on this. But we hope that we will not be hit too hard,” said Schuster who believes that the major reason for this envisaged slump is the government subsidies stipulated in the latest version of the German Renewable Energy Sources Act (EEG). These appear to be very attractive, but many details are extremely inaccurate. “To cite just one example, the new version states that the plants need to have a retention time of at least 150 days. However, this is derived from a regulation which explicitly stipulates an average retention time. It can be assumed that the new version implies the same. But what if 150 days refers to the absolute retention time? This inaccuracy would have far-reaching consequences. Biogas plants would need to be designed completely differently from the ones we are currently using,” said Michael Schuster, who is up in arms about the EEG. However, he hopes that the EEG Clearing House in Berlin will soon be able to solve this issue.

Despite all the bad forecasts for the biogas industry as a whole, n-bio is doing rather well. Schuster is planning to expand his company site in Konstanz. The market forecasts for Germany are one reason why many biogas companies are considering relocating to other countries. However, Michael Schuster is taking a relaxed approach for the time being. n-bio still has a technological lead, something that makes him quite optimistic for the future.

Further information:
n-bio GmbH
Michael Schuster (Managing Director)
Max-Stromeyer-Straße 116
78467 Konstanz
Tel.: +49 (0)7531/ 457 189 - 52
Fax: +49 (0)7531/ 457 189 - 9
E-mail: m.schuster(at)n-bio.de